Fatty acids are one of the principal components of lipids. In vivo, fatty acids are bonded to glycerin via an ester bond to form lipids (fats and oils) such as triacylglycerol. Further, many animals and plants also store and utilize fatty acids as an energy source. These fatty acids and lipids stored in animals and plants are widely utilized for food or industrial use.
For example, higher alcohol derivatives that are obtained by reducing higher fatty acids having approximately 12 to 18 carbon atoms are used as surfactants. Alkyl sulfuric acid ester salts, alkyl benzene sulfonic acid salts and the like are utilized as anionic surfactants. Further, polyoxyalkylene alkyl ethers, alkyl polyglycosides and the like are utilized as nonionic surfactants. These surfactants are used for detergents, disinfectants, or the like. Cationic surfactants such as alkylamine salts and mono- or dialkyl-quaternary amine salts, as other higher alcohol derivatives, are commonly used for fiber treatment agents, hair conditioning agents, disinfectants, or the like. Further, benzalkonium type quaternary ammonium salts are commonly used for disinfectants, antiseptics, or the like. Furthermore, lipids derived from plants are also used as raw materials of biodiesel fuels.
Fatty acids and lipids are widely used for various applications shown above, and therefore, it has been attempted to enhance the productivity of fatty acids or lipids in vivo by using plants and the like. Furthermore, the applications and usefulness of fatty acids depend on the number of carbon atoms. Therefore, controlling of the number of carbon atoms of the fatty acids, namely, a chain length thereof has also been attempted.
A fatty acid synthetic pathway of plants is localized in the chloroplast. In the chloroplast, an elongation reaction of the carbon chain is repeated starting from an acetyl-ACP (acyl-carrier-protein), and finally an acyl-ACP (a composite consisting of an acyl group being a fatty acid residue and an ACP) having 16 or 18 carbon atoms is synthesized. The synthesized acyl-ACP is formed into a free fatty acid by an acyl-ACP thioesterase (hereinafter, also simply referred to as “TE”). To the free fatty acid, CoA is bonded by an acyl-CoA synthetase. Then, the fatty acid acyl-CoA is incorporated into a glycerol skeleton by various acyltransferases, and is accumulated as triacylglycerol.
It is known that a glycerol-3-phosphate dehydrogenase (hereinafter, also simply referred to as “G3PDH”) plays a role of catalyzing a reaction of reducing dihydroxyacetone phosphate (DHAP) into glycerol-3-phosphate in a lipid synthesis to provide the glycerol skeleton. Thus, in order to cause accumulation of glycerolipids in plants or yeast, enhancement of expression of the G3PDH or modification of the G3PDH per se is proposed (see Patent Literatures 1 to 3 and Non-Patent Literature 1). Moreover, it is reported that an amount of lipids is increased by enhancing the expression of the G3PDH also in algae (see Non-Patent Literature 2).
Recently, algae attract attention due to its usefulness in biofuel production. The algae can produce lipids that can be used as the biodiesel fuels through photosynthesis, and do not compete with foods. Therefore, the algae attract attention as next-generation biomass resources. Moreover, it is also reported that the algae have higher lipid productivity and accumulation ability in comparison with plants. Research has started on a lipid synthesis and accumulation mechanism of the algae and lipid production technologies utilizing the mechanism, but unclear parts remain in many respects.